Hy4 Preview Is Now on Vercel AI Gateway, and It's Built for the Long Haul

Tencent's Hy4 Preview model is now available on Vercel's AI Gateway, and its headline feature, a one-million-token context window, makes it one of the most capable models you can drop into a vibe-coded project without wiring up a separate API account.

If you've been building AI-powered apps on Vercel and feeling the limits of shorter context windows, this is worth a closer look.

What Hy4 Preview Actually Is

Hy4 is an open-source model from Tencent. It uses a design called Mixture-of-Experts, which means the model has 770 billion total parameters but only activates 49 billion of them for any given piece of text. Think of it like a big team of specialists: not everyone works on every task, which keeps things efficient while still drawing on a huge pool of knowledge.

Vercel's changelog positions it for long-horizon coding, document analysis, game development, and scientific reasoning. That's a wide net, but the thread connecting all of those is complexity over time. Tasks that require holding a lot of context in mind at once, across many steps, or over very large documents.

The one-million-token context window is the real story. For reference, a typical novel runs around 100,000 words, or roughly 130,000 tokens. A million tokens means you could feed Hy4 a very large codebase, a thick legal document, or a long product specification and ask it to reason across the whole thing in a single pass.

Why This Matters if You're Just Starting to Build

The friction of switching between AI providers is real. Every new model usually means a new API key, a new authentication flow, new pricing to decode, and often a new SDK to learn. For designers building their first or second app, that overhead adds up fast and pulls focus away from the actual product.

AI Gateway removes most of that. It gives you one unified API for calling models from multiple providers, including Hy4 Preview now, and it passes through provider pricing with no markup and no platform fee on inference. You can even connect your own API keys through the Bring Your Own Key feature if you already have a Tencent or other provider account.

The gateway also handles retries and failover automatically, meaning if a provider has a blip, your app doesn't just break. For a solo designer shipping something real, that kind of reliability layer used to require meaningful engineering work to set up.

How to Actually Try It

The lowest-friction starting point is the model playground, which Vercel links directly from the Hy4 Preview model page. You can prompt it there before writing a single line of code, which is the right way to gut-check whether a model's output style suits your project.

When you're ready to wire it into an app, Vercel's AI SDK is the connector. You set the model identifier to tencent/hy4-preview and the gateway handles routing. No separate Tencent account required if you're using Gateway's own access.

The more interesting path for designers building tools is the coding agents setup. Vercel's AI Gateway supports a range of agents, including Cursor, Claude Code, Codex, and others. Once you run the setup command and select Hy4 Preview inside your agent, you're pointing a long-context model at your codebase. That's genuinely useful when you're asking an agent to refactor a sprawling component tree or understand a project that has grown beyond a few files.

For document-heavy product ideas, think a contract reviewer, a research summariser, or a feedback aggregator, the million-token window means you can hand the model a much larger chunk of source material than most alternatives allow.

What to Keep in Mind

Hy4 is still in preview. That word does real work here. Preview models can change, be rate-limited, or be deprecated without the same notice a stable release would get. It's a great model to experiment with and to prototype around, but probably not the one to pin a production feature to until it graduates out of preview status.

The model's strengths are listed as coding, document analysis, and scientific reasoning. If your app is more conversational or creative, you might find other models on AI Gateway fit better. The playground is free to use for exploration, so testing before committing is easy.

The bigger picture is that AI Gateway keeps expanding its model roster, and each addition costs you nothing extra to try. For designers building with AI, having a single place to audition models without juggling credentials is quietly one of the most useful things happening in the tooling ecosystem right now.

Hy4 Preview is a capable new option on a platform you're probably already using. That's a good combination.